1. Technical Field
Exemplary aspects of this disclosure generally relate to an image forming apparatus and image density control method, the image forming apparatus, such as a copier, a printer, a facsimile machine, a plotter, or a multifunction machine capable of at least two of these functions, to detect an image on an intermediate transfer member and control density of the forming image.
2. Description of the Related Art
In image forming apparatuses, such as a copier, a printer, a facsimile machine, a plotter, or a multifunction machine capable of at least two of these functions, the density of formed images may fluctuate due to such factors as usage environment, fluctuation in the characteristics of image carriers (photoreceptors) and developer over time, and manufacturing inconsistencies in the image carriers and the developer.
In image forming apparatuses including an intermediate transfer member (belt) on which the image is transferred from the image carrier, so-called process control is performed by detecting an image (adjustment pattern) on the intermediate transfer member.
In this configuration, an image density adjustment pattern for adjusting the density of the image is formed on the intermediate transfer member, light is directed onto the image density adjustment pattern, light reflected from the image density adjustment pattern is detected by a reflection-type density sensor, and one or more image forming conditions are controlled so that readings from the reflection-type density sensor assume a desired output value.
In order to perform such control accurately, it is necessary to adjust the intensity of the light that is used to illuminate the image density adjustment pattern. Conventionally, this may be done by directing light onto a clear, background surface of the intermediate transfer member, the light reflected from the background surface is detected by the reflection-type density sensor, and the image forming conditions are adjusted so that the readings from the reflection-type density sensor assume a desired value.
However, the surface of the intermediate transfer member may not be very glossy due to limitations placed on the type of material that can be used for the intermediate transfer member by the need to transfer the image carried on the intermediate transfer member onto a transfer sheet. Moreover, the glossiness of the surface of the intermediate transfer member may decline as the surface of the intermediate transfer member deteriorates over time. In such cases, the readings from the reflection-type density sensor may become insufficient to adjust correctly the intensity of the light directed onto the image density adjustment pattern.
In order to solve this problem, JP-2010-44098-A discloses a reflection-type density sensor that is movable in a direction orthogonal to a direction in which the intermediate transfer member moves, in other words, is movable in a width direction of the intermediate transfer member. The readings from the intermediate transfer member are set to a value that is sufficient to execute the above-described adjustment by moving the density sensor. This case assumes that the degradation in glossiness appears as unevenness in the width direction of the intermediate transfer member when the glossiness of the surface of the intermediate transfer member deteriorates over time, in which case this adjustment is executed by moving the reflection-type density sensor toward a portion that remains glossy enough to enable such adjustment.
However, although generally effective for its intended purpose, the above-described configuration is ineffective in a case in which the surface of the intermediate transfer member is not very glossy to begin with due to the limitations placed on the material of the intermediate transfer member as described above, and as a result, the surface has insufficient glossiness to enable adjustment of the readings from the reflection-type density sensor. In addition, in a configuration in which the reflection-type density sensor is movable, such a configuration is complicated and costly, and hinders efforts to make the image forming apparatus more compact.